I have no idea if this can be reproduced. It has only happened once so far, just happened. Lost the ability to use E on Lux
in a ranked match. It shows up as costing 0 mana, and wasn't lit up, or usable. I have two links. One of gameplay without the ability to use it, and then a short one of me showing the tooltip.
https://www.youtube.com/watch?v=Yhpd-xbubOM Also has some gameplay where it shows the icon never being lit up
It's a known bug that is rare and inconsistent, but has obvious impact on the game.
I am not sure if Riot is trying to fix it, but the issue was supposedly made aware at least a year ago. It is very inconsistent to reproduce though; I am guessing if you spam the skill key as you were dying, it has a higher chance of reproducing the bug. I don't know the cause behind the bug though. Maybe it's an error with the character finishing the cast time on their skills right as they died, and the system gets an error on whether to proceed with the ability's effects or not (or, that it is trying to proceed with the effects, but the system already registers you as dead, so there is a contradiction).
